This application relates generally to the field of heat sinks in an electrical apparatus. More specifically, this application relates to a metallic heat sink for a diode embedded therein of an electrical machine and a method of manufacturing the same.
Bridge rectifiers are used to rectify current output from alternative current sources, such as an alternating current generator. Bridge rectifiers for motor vehicle alternators are well known in the art and generally include two metal parts used as heat sinks that are electrically insulated from each other. As a result of the current which is transmitted therethrough, the bridge rectifier becomes heated due to the internal power loss on each individual diode. Thus, the bridge rectifier must be properly cooled in order to handle the maximum required current while still being tolerant to increased temperatures due to internal power losses.
Each of the metal parts or carrier plates includes semiconductor diodes which are arranged to polarize the two metal parts into respective positive and negative direct voltage output terminals. The diodes are then connected to respective phase windings of an output winding of the alternating current generator.
The rectifier diodes are connected to respective carrier plates, and these carrier plates are used as heat sinks for these diodes as well. The rectifier diodes are typically inserted by pressure in receiving bore holes of the carrier plate or heat sink, or are soldered to the carrier plate using appropriate solder alloys. The end wires connected to the rectifier diodes enable the rectifier diodes to be connected to external sources.
The heat sinks are typically constructed in the shape of a circle or crescent and are fastened in the same plane to the alternating current generator.
Various difficulties or problems have occurred using this standard diode rectifier. For example, one problem which has been experienced with diode rectifiers includes the need to carefully match the diode characteristics in order to avoid imbalance in the amount of current conducted by the individual diodes. If thermal imbalance is experienced, certain diodes will increase current flow which may result in thermal runaway. Thermal runaway involves a diode which is unable to regulate its current flow and temperature. In this situation, the diode conducts increased current and experiences increased temperature until the individual diode is no longer able to conduct such a high current or experience such a high temperature, and the diode becomes destroyed. Frequently, thermal runaway results in the destruction of an individual diode, and the destroyed diode becomes short circuited thereby rendering the entire bridge rectifier inoperative.
Another problem which has been encountered in bridge rectifiers is that the bridge rectifiers must not only be able to withstand normal battery charging current, but must also be able to supply current, perhaps as much as ten times the normal charging current. These increased current situations may occur, for example, when the motor vehicle is being started. Bridge rectifiers, as discussed, arc typically unable to absorb or conduct these types of excess currents and are also unable to rapidly dissipate the resulting heat. Thus, the heat generated within the bridge rectifier may destroy the individual diodes. In order for bridge rectifiers to handle these types of excessive currents and heat, it becomes necessary to utilize a bridge rectifier which has higher current handling capability. Due to the space limitations of the alternating current generator, it then becomes very difficult to provide such a bridge rectifier from a feasibility standpoint as well as at an economical cost.
A further attempt at increasing the current capacity and heat dissipating characteristics of the bridge rectifier includes the mounting of semiconductor diode chips onto first and second metallic heat sinks which are electrically insulated from each other by a thin sheet of electrical insulating material. The diode chips are then covered by a protective insulating coating after connection to the respective heat sink. One of the metallic heat sinks includes a finned area which is subjected to cooling air when the bridge rectifier is mounted to the generator. The heat sink with the plurality of fins includes twelve air passages. This type of bridge rectifier is shown in U.S. Pat. No. 4,606,000 to Steele et al., incorporated herein by reference.
FIGS. 1a-1b are illustrations of a prior art bridge rectifier as depicted in U.S. Pat. No. 4,606,000 to Steele et al. In FIG. 1a, combined alternator cover and carrier plate 12 includes carrier plate or heat sink 14 connected to alternator cover 16 (only partially depicted to expose underlying plate 14). Carrier plate 14 includes receiving bore holes 18 which are formed for receiving the diodes. Carrier plate 14 includes alternator mounting holes 20 for mounting carrier plate 14 to the alternator cover 16 via standard connection means such as a bolt or screw connection. Alternator cover 16 includes three main alternator air passages which interact with the twelve air passages 26 in carrier plate 14, thereby cooling radiating fins 23. As depicted in FIG. 1b, carrier plate 14 is of a rectangular shape (in side view) having receiving bore holes 18 configured therethrough to receive a press fit diode 22 (partially shown) disposed within carrier plate 14. The temperature of the heat sink around the diode base 24 is highest and a demand for more current from a generator directly translates to more current through diode 22. Higher current flow through a diode increases the temperature of diode 22, specifically at diode base 24. In current design, diodes frequently operate in the extreme limits of thermal conditions, necessitating enhancements in cooling to meet future demand of higher current therethrough for various applications.
FIG. 2 is an illustration of the positioning of the bridge rectifier 11 within a standard alternating current generator generally designated with reference letter G. As depicted in FIG. 2, the completely assembled bridge rectifier 11 which includes carrier plate 14 and cover 11 a is connected to alternator cover 16 via any standard connection means, such as screws 17. Reference numeral 13 denotes the bottom of carrier plate 14, while reference numeral 15 denotes the top of carrier plate 14. Bridge rectifier 11 is also connected to regulator 19. As mentioned previously, the standard bridge rectifier shown in Steele et al. and FIGS. 1a-1b are well known in the art.
While there have been, as described above, several attempts to increase the current and heat capacity of the bridge rectifier, none of these prior attempts have been completely satisfactory. That is, none of these prior art attempts have increased the current and heat capacity of the bridge rectifier in an economical manner.
As a result of the dissatisfaction with existing bridge rectifiers, there is a need to improve the performance characteristics of prior art bridge rectifiers. This problem resides in the poor performance characteristics of the carrier plate, and the resulting defects or failures which arise therefrom. In addition, there is a need for a carrier plate which increases the dissipation of heat from the diode and more efficiently cool the diode by facilitating increased surface area of the heat sink available to a diode resulting in an increased rate of dissipation of heat from the diode through the carrier plate in which the diode is disposed.
A method and apparatus for increasing the rate of heat dissipation from an object is disclosed. The apparatus includes a heat sink device for retaining the heat dissipating object including a substrate having an aperture configured therethrough to receive the object and an extruded portion extending from a surface of the substrate defining the aperture. The extruded portion is configured to receive the object and increase a surface area available for heat transfer from said object in said aperture relative to without said extruded portion.
The method includes forming an aperture in a portion of a substantially planar substrate. The aperture is sized to receive the object therein. The method further includes extruding an extruded portion from the portion of said substrate forming the aperture. The extruded portion extends from a surface of the substrate defining the aperture. The extruded portion is configured to receive the object and increase a surface area available for heat transfer from the object in the aperture relative to without the extruded portion.